Receiver circuits are used for both terrestrial and cable reception within televisions, digital video recorders, video cassette records, set-top box devices (such as cable and satellite tuners), frequency modulation (FM) radios, models, and other electronic devices. Some smart phones also utilize receiver circuits for television reception. In general, such receiver circuits include a tuner that selects a narrowband signal from within a wide or broadband signal having multiple channels. The tuner includes bandpass filters, amplifiers, and mixer circuits for selecting a desired channel and for rejecting unwanted channels, noise, and interference.
Television signals can be broadcast at a variety of different frequencies, including ultra-high frequency (UHF), very high frequency (VHF), and high frequency (HF) frequency bands. The International Telecommunications Union (ITU) defines the UHF frequency range as encompassing electromagnetic waves between 300 MHz and 3 GHz. VHF occupies frequencies within a range from approximately 30 MHz to 300 MHz, and HF occupies frequencies within a range from approximately 3 MHz to 30 MHz.
A television receiver processes terrestrial signals with high quality by including low noise amplifier circuits having an exceptional noise figure (NF), since the terrestrial signals generally have a significant signal power difference from channel to channel. Also, a television receiver processes cable television signals with circuits having a certain return loss (RL) to avoid attenuation in the received signal (and with an acceptable NF), since, in a cable environment, the power tends to be relatively even and well-controlled across the channels. In some emerging markets, a television receiver, and in particular, the corresponding circuits of the receiver need both good NF and RL to process quality cable television signals. At the same time, linearity also has to be high. However, some television receiver circuits can interfere with the operation of other corresponding receiver circuits, thus these circuits must accept trade-offs between a good noise figure, a good return loss, and linearity, since it is difficult to achieve all three parameters as desired.
The use of the same reference symbols in different drawings indicates similar or identical items.